EP0012914B1 - Coolant transfer coupling for an electric machine with superconducting rotor winding - Google Patents

Description

The invention relates to a coolant connection head for an electrical machine, which contains a rotor rotatably mounted about an axis with a superconducting winding to be frozen by a coolant, with a device for feeding the coolant from a non-rotating coolant line part into a rotating, with the Runner-connected coolant line part, which contains at least one sealing device which serves to seal an intermediate space formed between these line parts, and which in the operating state of the machine. predetermined leakage rate dependent on the prevailing pressure difference.

Such coolant connection heads are known from the literature "Advances in Cryogenic Engineering", vol. 23, New York 1978, pages 125 to 131 and from US-A-3 991 588.

To cool a superconducting winding in the rotor of an electrical machine, in particular a turbogenerator, devices for transferring a coolant between the rotor and fixed connecting lines must be provided. Via such a device, the coolant, for example liquid or gaseous helium, is fed to the winding in the rotor or is removed therefrom. The machine is therefore provided with a connection head which contains a corresponding transfer device. The design of this device, which is also referred to as a coupling, is particularly difficult, particularly with regard to the lowest possible thermal losses of the coolant circuit for the superconducting winding and with regard to small leakage rates of the coolant. The couplings must have rotating seals with relatively low friction, which on the one hand seal the coolant, in particular the liquid helium, against the outside and on the other hand separate the input and output sides within the rotating system. The sealing devices required for this must also allow radial and axial shaft play of the rotor and work trouble-free over longer periods, for example a few years.

The known coolant connection head contains a corresponding helium coupling. It is provided with a hollow cylindrical, stationary housing, into the interior of which a tubular feed line protrudes. The open end piece of this feed pipe is surrounded concentrically by an end piece of a conduit pipe which is firmly connected to the rotating parts of the machine, so that an annular space is formed between these two pipes. The concentric position of the two pipe sections within the housing is ensured by means of bearings provided for this purpose. In order to prevent the fed-in helium from escaping to the outside via the intermediate space, a seal with a predetermined gap is provided, for example (see FIG. 3). The gap is dimensioned such that contact between rotating and stationary parts of the transfer device is avoided in the event of radial and axial vibrations of the rotor shaft, so as to prevent frictional heat and wear of sealing parts. Since, in general, the seal gap cannot be made arbitrarily small, a certain leakage rate at the seal has to be accepted.

These leak rates on sealing devices with gaps between rotating and non-rotating, largely non-contact sealing parts can be kept relatively small if a so-called self-pumping effect in thermosiphon loops is used for the cooling system of the winding of the rotor (see the magazine "Cryogenics" , July 1977, pages 429 to 433 and DE-A1-2 530 100). Then the coolant is only to be fed into the rotor with a relatively low overpressure at the transfer device, so that there is a correspondingly small pressure difference at the sealing devices. However, this only applies to the cooling system in the cooled state. During the cooling phase of the winding and especially during the initial phase, the flow resistance of the cooling system is still very high. Since significantly higher coolant throughput rates are required to achieve acceptable cooling times than in the cooled state, i. H. the coolant must be introduced into the cooling system at a correspondingly higher pressure during these times, correspondingly large leakage losses of coolant occur during this cooling phase at these sealing devices.

FR-A-1 350 388 shows a sealing device with which a water circuit for the rotor of a turbogenerator is to be sealed from the outside air. When the water pressure drops, a further sealing device comes into operation, in which a sealing gap existing between the associated sealing surfaces is closed. The purpose of this known measure is to achieve complete tightness of the cooling circuit against the external atmosphere even when the machine is at a standstill and to enable the cooling circuit to be evacuated. This seal has u. a. Rubber beads, which is why the seal is unsuitable from the outset for sealing a cryogenic coolant, as is required for cooling superconducting windings.

The object of the present invention is to provide the coolant connection head of the type mentioned at the beginning with a device for transferring tion of a coolant from non-rotating to rotating coolant line parts so that the coolant losses at the sealing devices of its transfer device are relatively small during the cooling phase of the machine.

This object is achieved in that at least one further sealing device is provided for sealing the intermediate space, in which an existing sealing gap between the associated sealing surfaces can be adjusted from the outside in such a way that during the cooling phase of the machine at a relatively low speed and compared to the rated operation relatively high coolant throughput, a smallest sealing gap is set with a significantly increased flow resistance compared to the rest of the sealing device, which sealing gap is widened to a predetermined level before the transition to nominal operation.

The advantages of this design of the coolant connection head are, in particular, that during the cooling phase of the winding the sealing gap of the further sealing device can be kept so small that a correspondingly good sealing of the coolant takes place on it. During this cooling phase, the rotor of the machine is generally kept at a relatively low speed at most, so that only correspondingly low friction losses and wear devices can occur. Once the winding has cooled to the operating temperature and the coolant throughput has been reduced to a low final value, the sealing gap of the further sealing device can be widened again to a predetermined level. The sealing on the transfer device then takes place essentially only on the first sealing device, and the rotor of the machine can easily be brought to the nominal speed of the operating state.

According to an advantageous development of the coolant connection head according to the invention, the coolant line parts contain concentrically arranged, partially enclosing pipe end pieces and the further sealing device is provided on the end face of one of the pipe end pieces. At this point, the additional sealing device with its adjustable sealing gap can be arranged in a particularly simple manner.

Furthermore, the further sealing device can advantageously contain a non-rotating sealing part which contains the non-rotating sealing part which is mechanically connected to the non-rotating pipe end piece, and this pipe end piece can be displaceable in the axial direction within the non-rotating coolant line part. The sealing gap formed between the non-rotating sealing part and a rotating sealing part can thus be adjusted in a simple manner with the aid of a corresponding displacement of the non-rotating pipe end piece.

The further sealing device can also advantageously be a mechanical seal. Such seals are simple in construction and their sealing gap can be easily adjusted by choosing an appropriate distance between their sealing parts.

Further configurations of the coolant head according to the invention are characterized in the dependent claims.

An exemplary embodiment of a coolant connection head according to the invention is explained below with reference to the figure of the schematic drawing.

In the figure, only the upper half of a coolant connection head for the machine is illustrated as a longitudinal section. This machine, which is not shown in more detail in the figure, can in particular be a turbogenerator which contains a rotor with a superconducting field winding to be deep-frozen, which is surrounded by at least one co-rotating damper shield, which is generally also to be cooled. To reduce the heat input into the frozen winding, it is also surrounded by vacuum spaces. For this purpose, the entire rotor can be enclosed in a rotating vacuum housing (cf. DE-A1-2339772 and "Siemens Research and Development Reports", Volume 5 (1976), No. 1, pages 10 to 16). The rotor can also rotate in a vacuum room.

The coolant connection head of the machine, which is only partially shown in the figure, contains a fixed head part 2, into which the lateral end piece 3 of a shaft of the rotor rotatably mounted about an axis of rotation 4 projects. This shaft end piece is rigidly connected to the rotor (not shown in the figure) and is generally located on the side of the machine which is opposite the drive side. The shaft end piece 3 contains an outer hollow cylinder 6 at room temperature, which is arranged concentrically around an inner hollow cylinder 7, the end piece 8 of which projects a predetermined distance from the open end face 9 of the outer hollow cylinder 6. Between the outer hollow cylinder 6 and the inner hollow cylinder 7, two double tubes 11 and 12 are arranged concentrically so that an outer ring channel 13 between the outer double tube 11 and the outer hollow cylinder 6 and an inner ring channel 14 between the inner double tube 12 and the inner hollow cylinder 7 are trained. The two double tubes 11 and 12 delimit an annular space 16 radially outward. They each consist of two concentrically arranged hollow cylinders, which are sealed against one another on their end faces in a vacuum-tight manner. The inner spaces 17 and 18 thus formed between the two hollow cylinders of each double tube are for the sake of thermal insulation evacuated.

The connection head part 2 also contains a substantially hollow cylindrical, non-rotating outer housing 20, which encloses the end of the rotating outer hollow cylinder 6 of the shaft end piece 3 to a certain extent in the axial direction and is supported on this hollow cylinder 6 via a main bearing 22. In addition, the connection head part 2 contains an inner, essentially hollow cylindrical housing part 23 which concentrically surrounds the end piece 8 of the inner, rotating hollow cylinder 7 of the shaft end piece 3 and which is supported on the end piece 8 via a sub-bearing 25. This housing part 23 is rigidly connected to the outer housing 20 via an essentially annular disk-shaped end part 26. The parts 20, 23 and 26 of the connection head part 2 delimit an interior lying essentially in front of the end face 9 of the outer hollow cylinder 6 of the shaft end piece 3 within the connection head part 2. To seal this interior, parallel to the bearing 22 between the non-rotating outer housing 20 and a sealing system 29 is provided for the rotating hollow cylinder 6. In a corresponding manner, the inner housing part 23 is also sealed off from the end piece 8 of the inner hollow cylinder 7 by means of a sealing system 30. These sealing systems can be, for example, ferrofluidic seals, as are known from DE-A1-2 034 213.

At the connection head part 2, the supply and discharge of the coolant required for cooling the superconducting excitation winding, which is generally helium, is provided into and from the shaft section 3 of the rotor. For this purpose, liquid helium A is introduced into the annular space 16 between the double tubes 11 and 12 via a feed device 32. This device contains two double pipe pieces 33 and 34 protruding into the annular space 16 and arranged concentrically to the axis of rotation 4, between which an annular feed channel 35 is formed. This axially parallel feed channel is connected at its end projecting into the interior of the connection head part 2 to a radially extending feed channel 37 which is formed between two annular disk-shaped, double-walled line parts 38 and 39. This radial feed channel 37 is connected to a further feed channel 41, which runs parallel to the axis and whose distance from the axis of rotation 4 is greater than the corresponding distance of the feed channel 35. This feed channel 41, which is annular in cross section, is formed between two double pipe pieces 42 and 43 which protrude from the end part 26 of the connection head part 2 provided with a corresponding, sealed passage 44 and which are provided with a connection flange 45, to which by means of a connection not shown in the figure Connection line can be connected to a refrigeration device supplying the liquid helium A. Since all helium-carrying parts of the feed device 32 are double-walled, the spaces 47 and 48 between the adjacent walls can be evacuated to reduce the heat input to the liquid helium A.

According to the exemplary embodiment, the supply device 32 divides the interior space formed in the connection head part 2 and delimited by the components 20, 23, 26 into two separate subspaces 50 and 51. If necessary, however, these two subspaces can also be connected to one another, for example by providing, instead of the two double-walled line parts 38 and 39 of the feed device 32, a plurality of radially extending, mutually spaced-apart double pipe pieces.

In order to prevent a direct backflow of the liquid helium A fed into the annular space 16 into the partial spaces 50 and 51 of the interior of the connection head part 2, there is in the annular space 53 formed between the tubes 11 and 33 and in the corresponding annular space 54 between the tubes 12 and 34 at least one annular sealing device 56 or 57 is provided. These sealing devices, which are only indicated in the figure, can be, for example, labyrinth seals or lip seals. When the pressure gaps between the two sides of each sealing device are relatively small, only a relatively small portion of the helium A, designated A ₁ or A ₂ , enters its interior 50 or 51 of the connection head part 2 via its sealing gaps.

The helium, which is heated in the rotor of the machine and is labeled A ₃ and A _4, is also fed into these interior spaces 50 and 51 via the ring channels 13 and 14 and mixes there with the helium A and A ₂ , respectively. To discharge the helium mixture A "A ₃ from the interior 50, a flange 59 is provided on the outer housing 20 of the connection head part 2. In a corresponding manner, the helium mixture A ₂ , A _{4 is} removed from the interior 51 via a flange 60 in the end part 26 of the connection head part 2 Return lines for the coolant, not shown in the figure and connected to the cooling device, are connected to these flanges.

In the machine according to the exemplary embodiment according to the figure, it is assumed that the vacuums required for the thermal insulation of the cold parts of the rotor, in particular the superconducting field winding, are maintained by constantly pumping out corresponding vacuum spaces. For this purpose, the inner hollow cylinder 7 of the shaft end piece 3 serves as a rotating evacuation tube. The end piece 8 of this hollow cylinder therefore opens into a sub-chamber 62 of the connection head part 2 which is close to the axis and which is formed by the inner housing part 23, the end part 26 and the secondary bearing 25 or the Sealing system 30 is limited. To evacuate this subspace 62, the end part 26 is provided with a corresponding connecting flange 63, to which an external evacuation device can be connected. The sealing system 30 located between the hollow cylindrical housing part 23 and the end piece 8 of the evacuation tube 7 serves for the vacuum-tight sealing of the subspace 62 with respect to the interior 51 of the connection head part 2.

For cooling the excitation winding of the rotor of the machine is in the operating state, ie at a predetermined speed of the cooled rotor of for example 50 ^sec-I, the so-called self-pumping effect advantageous in thermosiphon loops are utilized. For this purpose, an appropriately designed cooling system must be provided with heat exchangers that are located over a large radius. The coolant emerging from the excitation winding enters this heat exchanger cold and warms up there to temperatures which are, for example, between about 100 and 300 K, before it is then returned to a smaller radius and discharged to the outside via the coolant transfer device of the connection head becomes. For example, in the operating state of a 2000 MVA generator with a helium throughput of approximately 5 to 10 g / sec, the pressure drop in this heat exchanger must remain limited to values below approximately 40 mbar so that the self-pumping effect leads to a desired temperature reduction in the field winding.

During the cooling phase of the machine, however, the flow resistances of these heat exchangers in particular have to be overcome. For example, pressure differences of the order of 1 to 2 bar are required in order to be able to pump the cooling quantities of approximately 100 g / sec required in the initial phase through the cooling system of the machine. However, such pressure differences initially lead to an approximately 10 to 20 times greater leak rate at the sealing devices 56 and 57 compared to the operating state, in which, for example, there is only a pressure difference of approximately 0.1 bar above the sealing devices. As a result of the cooling of the gaps in the sealing devices, a further reduction in their flow resistance and thus a further increase in leakage losses can occur.

According to the invention, the coolant connection head is therefore provided with further sealing devices which are intended to be effective during the cooling phase of the rotor. For this purpose, the annular space 53 containing the sealing device 56 and the annular space 54 containing the sealing device 57 are each additionally sealed with a mechanical seal 65 or 66 with respect to the interior 50 or 51. These mechanical seals are advantageously designed in such a way that they have sealing surfaces or sealing gaps located in planes that are radial with respect to the axis of rotation. They therefore each contain an annular disk-shaped component 67 or 68, which extends in the radial direction and slidably abuts the annular disk-shaped end face of the double tube 11 or the double tube 12. The mechanical seals 65 and 66 are advantageously fastened to the helium supply device 32. This feed device is designed to be displaceable in the direction parallel to the axis, so that it can be used to set the sealing gaps formed between the mechanical seals and the corresponding double pipes. The double pipe pieces 42 and 43 of the feed device 32 are therefore slidably guided through the sealed passage 44 of the end part 26. For sealing, for example, O-rings 71 and 72 are used between the double pipe pieces and the front part.

During the cooling of the excitation winding, wherein the rotor of the machine at most rotates sec- ^l at low speeds, for example 2, the helium supply apparatus is then so far axially pushed 32 to the connection head portion 2 in the direction of the rotor, until the annular members 67 and 68 of the mechanical seals 65 and 66 lie sealingly on the end faces of the double tubes 11 and 12, respectively. For this purpose, appropriately preloaded, bellows 74 and 75 arranged concentrically to one another can serve between the end part 26 and the connecting flange 45. The travel of the bellows can be limited to a predetermined, minimum length L via a stop 76. Since the cooling process takes place at a low rotor speed, the mechanical seals are not subject to any particular wear. Their sealing force is also maintained during the cooling phase with the aid of bellows 74 and 75, shrinkage effects due to the cooling being compensated for.

In the final phase of the cooling process, ie immediately before increasing the speed of the rotor to the nominal speed of, for example, 50 sec- ¹ , the feed device 32 with its mechanical seals 65 and 66 is then retracted so far in the axial direction, for example by correspondingly adjusting the stop 76 that a predetermined, minimum distance between the sealing surfaces on the mechanical seals 65 and 66 is maintained. The throughput quantity of coolant is then already reduced to a lower, stationary final value, and the leakage losses at the sealing devices 56 and 57 remain tolerable. When the machine rotates at the nominal speed, frictional heat on the sealing surfaces of the mechanical seals 65 and 66 and thus corresponding wear of these seals can be avoided in this way.

To ensure that the ring ring is evenly attached ben-shaped components 67 and 68 of the mechanical seals 65 and 66 on the end faces of the double tube 11 and the double tube 12 and thus to ensure at least approximately the same sealing properties of these seals, the mechanical seal 65 is rigidly attached to the double tube 33, while the mechanical seal 66 on the double tube 34 is displaceable to a predetermined extent. For this purpose, a prestressed bellows 78, which extends in the axial direction, is used between the annular disk-shaped line part 39 of the feed device 32 and the annular disk-shaped component 68 of the seal 66. This bellows also serves to seal the mechanical seal 66 with respect to the double pipe 34 Bellows or the advancement of the seal 66 on the double tube 12, a stop element 79 is attached to the double tube 12.

In the exemplary embodiment according to the figure, it was assumed that the coolant A is fed at a predetermined distance from the axis of rotation in the direction parallel to the axis from a stationary part into a rotating line. According to the invention, however, additional adjustable sealing devices can also be provided for a coolant connection head with a central coolant feed.

In the exemplary embodiment of the figure, it was also assumed that the annular spaces 53 and 54 were to be additionally sealed with a single sealing device 65 and 66 during the cooling phase. If necessary, however, several such sealing devices can also be provided for sealing each annular space.

The coolant connection head according to the invention is particularly suitable for runners with superconducting excitation windings, for the cooling of which the self-pumping effect is to be used and whose additional sealing devices have largely contactless gaps between rotating and non-rotating parts.

Claims (9)

1. A coolant connection head for an electrical maschine which includes a rotor mounted for rotation about an axis and having a superconductive winding which is to be cooled to a low temperature by a coolant, comprising apparatus for feeding the coolant from a non-rotating coolant supply line component into a rotating coolant supply line component which is connected to the rotor, which apparatus includes at least one sealing device (56, 57) which serves to seal an interspace (53, 54) located between these supply line components, and which, when the maschine is in the operating state, permits a predetermined rate of leakage which is dependent upon the pressure difference prevailing thereat, characterised in that for the sealing of the interspace (53 or 54), there is provides at least one further sealing device (65 or 66 respectively), in which a sealing gap present between the associated sealing surface can be adjusted from the exterior; in that during the cooling phase of the maschine, when, in contrast with normal operation, the rotation speed is relatively low and the coolant throughput is relatively high, a minimum sealing gap is set with a flow resistance which is substantially increased in comparison with the remainder of the sealing device, which sealing gap is widened to a predetermined extent before the transition to normal operation.

2. A coolant connection head according to Claim 1, characterised in that the coolant supply line components include tubular end components (33, 34 and 11, 12) which are arranged coaxially to one another and which partially surround one another; and that the additional sealing device (65,66) is arranged at the end face of one of the tubular end components.

3. A coolant connection head according to Claim 1 or Claim 2, characterised in that the additional sealing device (65, 66) is a sliding ring seal.

4. A coolant connection head according to one of Claims 1 to 3, characterised in that the additional sealing device (65, 66) has a sealing gap which runs in a plane radial to the axis of rotation (4).

5. A coolant connection head according to one of Claims 2 to 4, characterised in that the additional sealing device (65, 66) contains a non-rotating sealing element (67, 68) which is mechanically connected to the non-rotating tubular end component (33, 34); and that this tubular end component (33, 34) is displaceable in the axial direction in the non-rotating coolant supply line component (2).

6. A coolant connection head according to one of Claims 2 to 5, characterised in that the rotating sealing surface of the additional sealing device (65, 66) is located at the end face of the rotating tubular end component (11, 12).

7. A coolant connection head according to Claim 5 or Claim 6, characterised by a predetermined axial pressure of the sealing elements of the additional sealing device (65, 66), at a low rotation speed of the machine, on their common sealing surface produced by means of an appropriately prestressed spring system (74, 75) which acts upon the non-rotating tubular end component (33, 34).

8. A coolant connection head as claimed in Claim 7, characterised in that the maximum spring travel of the spring system (74, 75) is limited to a predetermined lenght (L) by an adjustable stop means (76).

9. A coolant connection head according to one of Claims 1 to 8, characterised in that the sealing gab of the additional sealing device (65, 66) can be adjusted, at the rated rotational speed of the maschine, by an adjustable stop means (76) to a determinate minimum interval between the sealing surfaces.

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